关键词: Polycrystalline silicon, Thermodynamics, Gas phase zinc reduction process, SiCl₂ generation ratio

Abstract: The modified Siemens process, which is the major process of producing polycrystalline silicon through current technologies, is a high temperature, slow, semi-batch process and the product is expensive primarily due to the large energy consumption. Therefore, the zinc reduction process, which can produce solar-grade silicon in a cost effective manner, should be redeveloped for these conditions. The SiCl₂ generation ratio, which stands for the degree of the side reactions, can be decomposed to SiCl₄ and ZnCl₂ in gas phase zinc atmosphere in the exit where the temperature is very low. Therefore, the lower SiCl₂ generation ratio is profitable with lower power consumption. Based on the thermodynamic data for the related pure substances, the relations of the SiCl₂ generation ratio and pressure, temperature and the feed molar ratio (n_Zn=n_SiCl4) are investigated and the graphs thereof are plotted. And the diagrams of K_p^Θ-T at standard atmosphere pressure have been plotted to account for the influence of temperature on the SiCl₂ generation ratio. Furthermore, the diagram of K_p^Θ-T at different pressures have also been plotted to give an interpretation of the influence of pressure on the SiCl₂ generation ratio. The results show that SiCl₂ generation ratio increases with increasing temperature, and the higher pressure and excess gas phase zinc can restrict SiCl₂ generation ratio. Finally, suitable operational conditions in the practical process of polycrystalline silicon manufacture by gas phase zinc reduction of SiCl₄ have been establishedwith 1200 K, 0.2MPa and the feedmolar ratio (n_Zn=n_SiCl4) of 4 at the entrance.Under these conditions, SiCl₂ generation ratio is very low, which indicates that the side reactions can be restricted and the energy consumption is reasonable.

Key words: Polycrystalline silicon, Thermodynamics, Gas phase zinc reduction process, SiCl₂ generation ratio